For the first time in three years, Merck can now say that all of its pediatric vaccines are again available. The disclosure, which was made on its supply status web page on Aug. 2, follows a series of components shortages and manufacturing gaffes that continue to leave some adult vaccines unavailable.

The drugmaker is once again shipping Comvax, a combination vaccine that is used to ward off meningitis and hepatitis B. Earlier this year, Merck restored supplies of PedvaxHIB for meningitis; ProQuad, which vaccinates against measles, mumps, rubella and chickenpox; and the pediatric formulation of hepatitis B vaccine Recombivax HB.

However, Merck continues to have difficulties with some of its adult vaccines. As previously noted, the adult version of Recombivax will not be available at all this year, after the drugmaker had hope to restore supplies by mid-2010 (back story). And orders placed for the Zostavax shingles vaccine after mid-May won’t be filled until November or December.

Merck has struggled with vaccine production issues for more than two years. The FDA issued a warning letter in April 2008 (see here) after an inspection found a ” number of significant objectionable conditions relating to your firm’s compliance” with good manufacturing practices. Throw in the difficulties Merck is having growing the market for its Gardasil vaccine for HPV and the drugmaker is likely to see overall vaccine sales decline to $3.1 billion this year, from $3.6 billion last year, but rebound to $3.4 billion next year, Deutsche Bank analyst Barbara Ryan tells Dow Jones.